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What is an Impact Value?
An impact value is an index which is calculated by looking at the percentage of winners that possess a particular characteristic when compared to the percentage of winners from the group as a whole. This is the generally agreed definition.
To make this clearer let us look at the following example:
Type of race/Location: Open class handicaps in Sydney and Melbourne (excluding Welters and Highweights)
Distance range: 1200m to 1399m
Type of horse: male gallopers, 4yo to 6yo
Variable: Finish position at last start.
In a 10 year time span there were 2967 runners that met the above conditions, and from these there were 259 winners, producing an 8.7% win rate.
Posn wins runs win% Ival
1 64 542 11.8% 1.35
2-3 72 687 10.5% 1.20
4-9 97 1264 7.7% 0.88
>9 26 474 5.5% 0.63
total 259 2967 8.7%
Again, an impact value is calculated by dividing the percentage of winners with a particular characteristic by the percentage of starters with that characteristic.
Let us assume that the characteristic in which we are interested from the above groups is that of last start winners.
We can see that there were 64 horses that had finished 1st at their last start that that won, out of a total of 259 winners from all of the groups. So the percentage of all the winners with that particular characteristic is 64/259 = 24.7%.
Next we find what percentage of the total runners had that characteristic. Here we can see that of the total number of 2967 horses there were 542 that had finished 1st last start. Therefore, the percentage of starters with that characteristic is 542/2967 = 18.3%.
Finally, to calculate the impact value you divide the percentage of winners with a particular characteristic, which is 24.7% for last start winners, by the percentage this sub-group formed as part of the group as a whole, here the last start winners make up 18.3% of the total number of runners.
Thus … 24.7% / 18.3% = 1.35 = the impact value
An impact value of 1.0 means that the horses with a particular characteristic won a percentage of their races that was equal to the percentage they were of the total number of runners in the group. For example, they won 16% of their races and they made up 16% of the total number of runners. Thus 16%/16% = 1, an impact value of one.Thus we can say that horses in this sub-group won exactly their "fair share" of the races won by runners in the groups as a whole.
As the worked example above showed an impact value of 1.35 we can interpret it as telling us that as last start winners this particular group of 4yo-6yo male gallopers, when competing in this type of open class races in Sydney, has historically won 1.35 times their fair share of races, compared to other 4yo-6yo male gallopers on the Sydney scene.
Compare this to those horses in the above table that finished 10th or worse last start, the latter group winning only 0.63 of their share of the races.
This is a useful way to view the significance of the impact value. It shows whether horses possessing a specific characteristic (eg back in 7 days or less, last start winner, beaten 3.1 to 5 lengths last start etc) have won more than their fair share of the races when compared to the group as a whole.
I readily concede that the actual example chosen to illustrate the meaning of the impact value sheds no new light on our understanding of the importance of good recent form. We all "know" that last start winners are likely to outperform horses that were 10th or worse last start. However, when it comes to days since last run etc, the impact values provide an insight that is not normally available.
In the normal course of processing, my computers calculate impact values for over 100 different variables. This mass of data is really overwhelming. Therefore, I have developed what I call composite impact values and that is what I am publishing in the Wizard.
For example, rather than listing various impact values for (say) days since last run, runs from a spell, beaten margin last start etc etc, I combine a number of the individual impact values that I have found relate directly to (say) fitness and use this composite impact value to report on the significance of the fitness profile of each horse.
In the [edited] three major factors are currently covered by impact values… fitness, form, and distance. At this stage I don’t plan to add more factors, just concentrate on these fundamentals. There is time to add more later.
In producing the [edited] impact values I have grouped horses by age and sex in the following way:
2yo colts and geldings
2yo fillies
3yo colts and geldings
3yo fillies
4yo, 5yo, 6yo horses and geldings
4yo, 5yo, 6yo mares
7yo and older horses and geldings
7yo and older mares
So when you see an impact value against a horse you know that this is the impact value that applies to horses of that particular age and sex, recorded in the class of race being contested tomorrow, over a distance within 10% of the distance of tomorrow’s race, and in the same location.
(Note: Location is determined by the way I have broken Australian racing into various levels of competitiveness for purposes of analysis and comparison.)
For example, if we had a 3yo colt (or gelding) contesting a welter handicap over 1600m at Randwick, the Wizard impact value would show how, over the past 10 years, 3yo colts and geldings have performed in 1600m (+/- 10%) welters run on all Sydney metropolitan tracks when possessing the same fitness, form, and distance ability characteristics (profile) possessed by this 3yo runner.
Taking this explanation a step further, if the 3yo was having his 4th run from a spell, was back in 21 days since his last run, was beaten less than 3 lengths at his last start etc, it is this fitness profile that is being reflected in his [edited] fitness impact value.
If the [edited] impact value in this case was 1.40 we can say that the group of 3yo colts and geldings (of which this horse is a member) possessing this particular fitness profile has performed very successfully, winning 1.4 times its fair share of this type of race when compared to all 3yo’s which have similarly competed.
So with the [edited] impact value you are able to see at a glance how certain age/sex groups have previously performed in the forthcoming class/distance/location. Before now this has never been possible. The Wizard now makes the impossible, possible.
This has been a necessarily short introduction to the [edited] impact values.
Warren Block, publisher
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Infamously another site used impact values and rated a heavy odds on chance at 500/1. The horse won easily. 
It is not the value itself which is easy, but how it is effectively used when combined with factors.
Knowing what to combine and what not to is more important than any one impact value.
Horseracing is far harder to evaluated than soccer or tennis or any other sport, because there are hundreds of extra variables. |